Decaying radioactive particles in solid rock cause spherical zones of damage to the surrounding crystal structure. A speck of radioactive element such as Uranium-238, for example, will leave a sphere of discoloration of characteristically different radius for each element it produces in its decay chain to lead-206. Viewed in cross-section with a microscope, these spheres appear as rings called radiohalos. Dr. Gentry has researched radiohalos for many years, and published his results in leading scientific journals.
Some of the intermediate decay products - such as the polonium isotopes - have very short half-lives (they decay quickly). For example, Po has a half-life of just 3 minutes. Curiously, rings created by polonium decay are often found embedded in crystals without the parent uranium halos. Now the polonium has to get into the rock before the rock solidifies, but it cannot derive from a uranium speck in the solid rock, otherwise there would be a uranium halo. Either the polonium was created (primordial, not derived from uranium), or there have been radical changes in decay rates in the past.
Gentry has addressed all attempts to criticize his work. There have been many attempts, because the orphan halos speak of conditions in the past, either at creation or after, perhaps even during the flood, which do not fit with the uniformitarian view of the past, which is the basis of the radiometric dating systems. Whatever process was responsible for the halos could be a key also to understanding radiometric dating.
Source: The Answers Book, by Ken Ham, Jonathan Sarfati, Carl Wieland, pp. 90-91.
